The present invention relates generally to underground drilling machines. More particularly, the present invention relates to underground drilling machines for use in horizontal directional drilling.
Utility lines for water, electricity, gas, telephone and cable television are often run underground for reasons of safety and aesthetics. Sometimes, the underground utilities can be buried in a trench that is then back filled. However, trenching can be time consuming and can cause substantial damage to existing structures or roadways. Consequently, alternative techniques such as horizontal directional drilling (HDD) are becoming increasingly more popular.
A typical horizontal directional drilling machine includes a frame on which is mounted a drive mechanism that can be slidably moved along the longitudinal axis of the frame. The drive mechanism is adapted to rotate a drill string about its longitudinal axis. Sliding movement of the drive mechanism along the frame, in concert with the rotation of the drill string, causes the drill string to be longitudinally advanced into or withdrawn from the ground.
In a typical horizontal directional drilling sequence, the horizontal directional drilling machine drills a hole into the ground at an oblique angle with respect to the ground surface. During drilling, drilling fluid can be pumped through the drill string, over a drill head (e.g., a cutting or boring tool) at the end of the drill string, and back up through the hole to remove cuttings and dirt. After the drill head reaches a desired depth, the drill head is then directed along a substantially horizontal path to create a horizontal hole. After the desired length of hole has been drilled, the drill head is then directed upwards to break through the ground surface. A reamer is then attached to the drill string which is pulled back through the hole, thus reaming out the hole to a larger diameter. It is common to attach a utility line or other conduit to the drill string so that it is dragged through the hole along with the reamer.
To drill relatively long holes, it is common to use drill strings having many interconnected lengths of drill pipe. The individual pieces of pipe are typically threaded together to form the drill string. When two drill pipes are threaded together, they are torqued to a predetermined torque (i.e., the makeup torque) to provide a secure connection. During drilling operations, the drill string is typically rotated in a forward direction (e.g., clockwise). Thus, assuming the pipes have right-hand threads, the forward rotation of the drill string encourages the pipes to remain threaded together. However, at times it is desirable to rotate the drill string in a reverse direction (e.g., counterclockwise). During this reverse rotation, the drill pipes are encouraged to become uncoupled. This is particularly true if the drill head of the drill string becomes wedged in hard soil or rock. If two of the drill pipes become uncoupled, a gap is formed in the threaded joint between the pipes that allows foreign matter to enter the joint. Until the foreign matter is removed, the matter can prevent the joint from being sufficiently retorqued. The loose joint will not be able to carry any reverse rotational torque load unless it is retorqued. If the uncoupling occurs underground, it may be difficult to identify that a joint has become loose and the operation and/or steering of the horizontal directional drilling machine can be negatively effected.
One aspect of the present invention relates to a horizontal drilling machine for directionally drilling a drill string into the ground. The drill string includes a plurality of elongated members threaded together in an end-to-end relationship. The drilling machine includes a track, and a rotational driver for rotating the drill string in forward and reverse directions about a longitudinal axis of the drill string. The drill string is rotated in the forward direction to thread the elongated members together. The drill string is rotated in the reverse direction to unthread the elongated members from one another. The drilling machine further includes a thrust mechanism for propelling the rotational driver along the track, and a reverse torque limiter that prevents the rotational driver from applying a reverse torque to the drill string that exceeds a reverse torque limit. The reverse torque limit is less than a maximum reverse torque that can be generated by the rotational driver, and is preferably less than a break-out torque required to uncouple the elongated members. In certain embodiments, a forward torque limiter can be used in combination with the reverse torque limiter.
Another aspect of the present invention relates to a horizontal drilling machine having a thrust limiter that can be activated and deactivated by an operator of the drilling machine depending upon drilling conditions encountered by the operator.
A further aspect of the present invention relates to a method for directionally drilling a drill string into the ground. The drill string including a plurality of elongated members. The method includes threading the elongated members together by applying forward torque to the elongated members, and pushing the drill string into the ground. The method also includes rotating the drill string in forward and reverse directions by applying forward and reverse torque to the drill string in an alternating fashion while thrust concurrently is applied to the drill string. The method further includes automatically limiting the reverse torque applied to the drill string to a value less than a break out torque required to uncouple the elongated members.
Still another aspect of the present invention relates to another method for directionally drilling a drill string into the ground. The method includes activating a reverse rotation torque limiter, and pushing the drill string into the ground. The method also includes rotating the underground drill string in forward and reverse directions by applying forward and reverse torque to the drill string in an alternating fashion while the reverse rotation torque limiter is concurrently activated. The reverse rotation torque limiter limits the reverse torque applied to the drill string to a value less than a break out torque required to uncouple the elongated members.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of the invention as claimed.